PEO coating on Mg screws

Abstract

The present invention relates generally to a bio-degradable implant based on magnesium having a reduced corrosion rate and to a method for the production of such an implant. It is a method for treating a surface of a bio-degradable metallic implant comprising the following steps: providing a dispersed system comprising a colloid-dispersed apatite and adding an apatite powder to the dispersed system, subjecting an implant to the dispersed system such that a surface of the implant which is to be treated is immersed in the dispersed system wherein the implant comprises a magnesium based alloy, applying an AC voltage difference between the implant as a first electrode and a second electrode positioned in the dispersed system for generating a plasma electrolytic oxidation on the immersed surface of the implant so that the immersed surface is converted to an oxide film which is at least partially covered by apatites formed by the colloid-dispersed apatite and the apatite powder. The evolution of corrosion induced hydrogen gas evolution is decreased and osseointegration is improved.

What is claimed is: 
     
       1. An implant comprising a biodegradable magnesium-based alloy, having a treated surface wherein
 the treated surface is at least partially converted to an oxide film by plasma electrolytic oxidation using a dispersed system comprising a colloid-dispersed apatite and 
 an apatite powder wherein 
 the converted surface is partially covered by apatite originating at least from the colloid-dispersed apatite and the apatite powder wherein 
 said biodegradable magnesium-based alloy has a treated surface with an oxide layer wherein 
 said oxide layer has an apatite covering wherein 
 the colloid-dispersed apatite has an average particle size of 100 nm or less 
 and wherein the apatite powder has an average particle size of 10 μm to 100 μm. 
 
     
     
       2. The implant according to  claim 1 , wherein the colloid-dispersed apatite or the apatite powder comprises hydroxyl-apatite or substituted hydroxyl-apatite. 
     
     
       3. The implant according to  claim 1 , wherein at least one metal oxide or at least one metal hydroxide or at least one metal phosphate containing compound is at least partially deposited onto the converted surface or embedded in converted surface. 
     
     
       4. The implant according to  claim 3 , wherein a metal of the metal oxide, a metal of the metal hydroxide or a metal of the metal phosphate containing compound is at least one metal selected from a group consisting of sodium, potassium, magnesium, calcium, zinc, copper, silver, zirconium, aluminum, silicon and at least one constituent of a material of the implant. 
     
     
       5. The implant according to  claim 1 , having a controlled degradation. 
     
     
       6. The implant according to  claim 1  characterized by a hydrogen gas evolution rate of less than or equal to 1 ml/cm −2 day −1  or a degradation rate of less than or equal to 100 mpy. 
     
     
       7. The implant according to  claim 1 , characterized in that said apatite powder is a precipitated and agglomerated colloid dispersed apatite. 
     
     
       8. The implant according to  claim 1 , characterized in that said oxide film has a thickness of 1 μm to 100 μm. 
     
     
       9. The implant according to  claim 1 , characterized in that said implant has an apatite covering with a thickness of 1 nm to 1000 nm. 
     
     
       10. The implant according to  claim 1 , characterized in that said implant has an apatite covering which forms a coral-like structure. 
     
     
       11. The implant according to  claim 1 , characterized in that said coral-like structure is formed from hydroxyl-apatite crystals which are bonded together. 
     
     
       12. The implant according to  claim 1 , characterized in that said implant has an apatite covering which forms an island-like structure on the converted surface. 
     
     
       13. The implant according to  claim 12  characterized in that said islands have an average size of less than 3000 nm. 
     
     
       14. The implant according to  claim 1 , characterized in that said implant is embodied as a plate. 
     
     
       15. An implant being produced with a method for treating a surface of a bio-degradable metallic implant, said method comprising the following steps: providing a dispersed system comprising a colloid-dispersed apatite and adding an apatite powder to the dispersed system,
 wherein the colloid-dispersed apatite is provided by precipitation and has an average particle size of 100 nm or less, 
 wherein the apatite powder has an average particle size of 20 μm to 100 μm, 
 subjecting an implant to the dispersed system such that a surface of the implant which is to be treated is immersed in the dispersed system, 
 applying an AC voltage difference between the implant as a first electrode and a second electrode positioned in the dispersed system for generating a plasma electrolytic oxidation on the immersed surface of the implant so that the immersed surface is converted to an oxide film which is at least partially covered by apatites formed at least by the colloid-dispersed apatite and the apatite powder, 
 wherein a treated surface with an oxide layer which has an apatite covering is formed.